The Internet, like so many other high tech developments, grew from research originally performed by the United States Department of Defense. In the 1960s, the military had accumulated a large collection of incompatible computer networks. Computers on these different networks could not communicate with other computers across their network boundaries.
In the 1960s, the Defense Department wanted to develop a communication system that would permit communication between these different computer networks. Recognizing that a single, centralized communication system would be vulnerable to attacks or sabotage, the Defense Department required that the communication system be decentralized with no critical services concentrated in vulnerable failure points. In order to achieve this goal, the Defense Department established a decentralized standard communication protocol for communication between their computer networks.
A few years later, the National Science Foundation (NSF) wanted to facilitate communication between incompatible network computers at various research institutions across the country. The NSF adopted the Defense Department's protocol for communication, and this combination of research computer networks would eventually evolve into the Internet.
Internet Protocols
The Defense Department's communication protocol governing data transmission between different networks was called the Internet Protocol (IP) standard. The IP standard has been widely adopted for the transmission of discrete information packets across network boundaries. In fact, the IP standard is the standard protocol governing communications between computers and networks on the Internet.
The IP standard identifies the types of services to be provided to users and specifies the mechanisms needed to support these services. The IP standard also specifies the upper and lower system interfaces, defines the services to be provided on these interfaces, and outlines the execution environment for services needed in the system.
In a typical Internet-based communication scenario, data is transmitted from an originating communication device on a first network across a transmission medium to a destination communication device on a second network. After receipt at the second network, the packet is routed through the network to a destination communication device using standard addressing and routing protocols. Because of the standard protocols in Internet communications, the IP protocol on the destination communication device decodes the transmitted information into the original information transmitted by the originating device.
The IP-Based Mobility System
The Internet protocols were originally developed with an assumption that Internet users would be connected to a single, fixed network. With the advent of cellular wireless communication systems using mobile communication devices, the movement of Internet users within a network and across network boundaries has become common. Because of this highly mobile Internet usage, the implicit design assumption of the Internet protocols (e.g. a fixed user location) is violated by the mobility of the user.
In an IP-based mobile communication system, the mobile communication device (e.g. cellular phone, pager, computer, etc.) can be called a mobile node or mobile station. Typically, a mobile station maintains connectivity to its home network while operating on a visited network. The mobile station will always be associated with its home network for IP addressing purposes and will have information routed to it by routers located on the home and visited networks.
Packet-Based Communication Systems
In Internet Protocol (IP) networks, the communication process is very different from prior conventional telecommunication systems. In an IP network communication, there is no open switched connection established between the caller and recipient devices. The information being transmitted between the caller and recipient devices is broken into packets of data, and each packet of data is transmitted to the recipient device in pieces. The data packets individually contain routing information to direct each packet to the recipient device. These packets are then reassembled into a coherent stream of data at the recipient device.
Code Division Multiple Access (CDMA) is an evolving third generation communication system standard for wireless communication systems that can transmit multimedia services using the packet-based Internet protocol. These CDMA mobile communication systems support multimedia telecommunication services delivering voice (VoIP) and data, to include pictures, video communications, and other multimedia information over mobile wireless connections. These types of communications are typically time-sensitive and require high data rate transfers with inherent delays minimized as much as possible.
As the capability of the various communication standards have improved, there has been an increasing need for high-speed transmissions and increased user capacity. A new CDMA packet air interface has been developed that offers improvements over earlier CDMA systems by implementing high-speed shared-traffic packet data channels on the forward air-link connection. Recent developments include CDMA-based 1xEV systems operating at 1.25 MHz. The 1.25 MHz carrier delivers high data rates and increased voice capacity. 1 xEV is a two-phase strategy. One phase is designated 1xEV-DO, which handles data only. The 1xEV-DO standard provides user with peak data rates of 3.0 Mbits/s. The other phase is 1xEV-DV, for data and voice. Other standards are evolving that also make use of the shared packet channel and multiplex packet communication for high-speed data and voice communication.
In the CDMA standard, Mobile Nodes, or Access Terminals (AT), roam within and across cellular communication sites. Each of the sites, or cells, possesses one or more transceivers coupled to a Base Transceiver Station (BTS) onto the communication network. The BTSs are in turn coupled to an Access Network. As an AT migrates across cellular borders, its BTS physical connection changes. An AT can be physically located anywhere on the network or sub-network, and its routing address data will change and require updating on other nodes. Wireless IP networks handle the mobile nature of AT with hand-off procedures designed to update the communication network and sub-network with the location of the mobile node for packet routing purposes. The latency period in these hand-offs can be prohibitively high. Call setup times can also be excessive as communication pathways are established before transmitting application data.
A new method of delivering application signaling (for example, SIP signaling) to setup a real-time application call like a Push-to-Talk (PTT) call in 1 xEV-DO can significantly reduce the call setup time. Call setup time is an important performance indicator for applications like Push-to-Talk (PTT), Voice over IP (VoIP) and Video Telephony (VT). At the same time, it minimizes the air-link and network resource utilization.
The method for delivering application signaling to setup a real-time application call (like PTT) determines the call setup time. Some methods of delivering application signaling so as to reduce call setup time normally require more air-link and network resource utilization, while other methods attempting to reduce the air-link and network resource utilization often lead to longer call setup time.
The application signaling for call setup can be accomplished in different ways. One method is to setup an air-link connection (or traffic channel) first and then deliver the application signaling over the traffic channel to the specific access terminal (AT). However, this approach invariably results in longer call setup time. In 1xEV-DO, the application signaling can be sent in the form of Data over Signaling (DoS) before a traffic channel is established. Application data destined for a dormant AT is transmitted as a broadcast message to all sectors within a paging zone using the signaling channel. Sending application data over the signaling channel, such as DoS protocol in 1xEV-DO access technology, typically requires a message 10 to 20 times larger than a regular page message (e.g. 211 bytes of application data versus 13 bytes of page message). The page message and application packet may be bundled together, or the application data may be sent separately to indicate a page to the AT. This leads to an overload in the signaling channel used for sending the page message, which for 1xEV-DO is the control channel. Using the control channel for sending application data decreases the bandwidth for sending 10-20 other page messages. The resulting control channel degradation will increase the call blocking rate.
Using DoS, the application signaling can be broadcast to the entire paging zone over the control channel along with the Page message, reducing the call setup time. However, since the application signaling messages are normally much larger than the Page message, the control channel utilization is increased significantly. More significantly, when the paging zone is large, the control channels of many sectors (all the sectors in the paging zone) are impacted. In 1xEV-DO, the forward link uses time division multiplex and the time slots are shared by the traffic channel and the control channel. The increase in control channel usage means a decrease in throughput or capacity as more time slots are devoted to the control channel to the detriment of the traffic channel.
In order to minimize the control channel usage, one approach is to page the AT first. After the access network (AN) receives a page response, the AT's location is known and the application signaling can be sent in the sector that receives the AT's page response. However, this method has the disadvantage of longer call setup time. There is a need for a new method of delivering application signaling that can reduce the call setup time while minimizing the air-link and network resource utilization.